Electro-optic polymer devices having high performance claddings, and methods of preparing the same

ABSTRACT

Electro-optic (EO) devices having an EO polymer core comprising a first host polymer and a first nonlinear optical chromophore (NLOC); and a cladding comprising a second host polymer and a second NLOC, and methods of preparing the same; wherein the first NLOC has a first bridge covalently bonded to an electron-accepting group and an electron-donating group; wherein the second NLOC has a second bridge covalently bonded to an electron-accepting group and an electron-donating group; and wherein the second bridge is less conjugated than the first bridge such that the cladding has an index of refraction that is less than that of the EO polymer core, and wherein the second NLOC is present in the second host polymer in a concentration such that the cladding has a conductivity equal to or greater than at least 10% of the conductivity of the EO polymer core at a poling temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application No. 62/732,143, filed on Sep. 17, 2018,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Electro-optic polymer devices include, for example, waveguides andmodulators. Electro-optic polymer devices and the use of organic secondorder non-linear optical polymers in such devices is well documented. Atypical electro-optic polymer modulator can comprise: 1) anelectro-optic polymer core; 2) a first polymer cladding overlying theelectro-optic polymer core; 3) a second polymer cladding underlying theelectro-optic polymer core; 4) a top electrode overlying the firstpolymer cladding; 5) a bottom electrode underlying the second polymercladding; and 6) a substrate such as silicon. In a typical electro-opticpolymer device, the total thickness of the core, first cladding, andsecond cladding can be around 6-10 μm. Typically, the refractive indicesof the polymer clads are chosen to confine a great majority of theoptical field in the electro-optic polymer core and keep the opticalfield from contacting the metal electrodes.

Thin film electro-optic polymer devices generally comprise multipleadjacent thin films that can be formed by, for example, spin coating. Inthe production of thin film electro-optic polymer devices, it can bedesirable to build successive layers of material with slightly differentoptical properties, such as refractive indices, in order to tailor theoptical properties of the particular device. The refractive index of acore layer must be higher than the refractive index of cladding layersso that the optical modes can be conducted into the core layer byinternal reflection.

Thereafter, a poling process is carried out to align the electro-opticpolymers in the core. Poling processes include the application of heatto soften the polymer host of the core layer and the application of avoltage across the device, such that the electro-optic polymers can bealigned.

Proper conductivity in the claddings of an electro-optic device duringpoling is also advantageous. The insulating properties of some polymersdetract from their desirable use as claddings in electro-optic polymerdevices because their low conductivities can result in the need forexcessive voltage to be applied across the device.

Additionally, it is beneficial to have solvent compatibility andadherence between layers, along with matching of thermal expansioncoefficients. Lastly, claddings should also exhibit low optical and RFloss.

Thus, it is desirable to provide electro-optic polymer devices havingcladdings which exhibit desirable conductivity at poling temperatures,indices of refraction lower than the core, low optical loss, low RFloss, solvent compatibility, thermal expansion coefficient matching andgood adherence between layers.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed, in general, electro-optic polymerdevices. More particularly, the present invention is directed toelectro-optic polymer devices having claddings with high performance andmethods of preparing such devices and cladding layers. Variousembodiments of the present invention provide claddings for electro-opticpolymer devices (e.g., waveguides, modulators, etc.) with significantlyimproved performance, including low optical loss, low RF loss, solventcompatibility, thermal expansion coefficient matching and good adherencebetween layers, in conjunction with the requisite difference in index ofrefraction and excellent conductivity at poling temperatures. Morespecifically, various embodiments of the present invention providecladdings which have a conductivity greater than or equal to at least10% of the conductivity of the electro-optic core material or in variousembodiments greater than or equal to the conductivity of theelectro-optic core material at a poling temperature, thus providing forefficient poling across the core without applying an excessively highvoltage across the device, and simultaneously, an index of refractionsuitable for a single mode device.

One embodiment of the present invention includes an electro-optic devicecomprising: (i) an electro-optic polymer core comprising a first hostpolymer and a first nonlinear optical chromophore; and (ii) a claddingcomprising a second host polymer and a second nonlinear opticalchromophore; wherein the first nonlinear optical chromophore has astructure according to the general formula (I):

D-Π-A  (I)

wherein D represents a first organic electron-donating group; Arepresents a first organic electron-accepting group having an electronaffinity greater than the electron affinity of D; and Π represents afirst bridge covalently bonded to A and D; wherein the second nonlinearoptical chromophore has a structure according to the general formula(II):

D′-Π′-A′  (II)

wherein D′ represents a second organic electron-donating group; A′represents a second organic electron-accepting group having an electronaffinity greater than the electron affinity of D′; and Π′ represents asecond bridge covalently bonded to A′ and D′; and wherein the claddinghas an index of refraction that is less than an index of refraction ofthe electro-optic polymer core, and wherein the second nonlinear opticalchromophore is present in the second host polymer in a concentrationsuch that the cladding has a conductivity equal to or greater than atleast 10% of the conductivity of the electro-optic polymer core at apoling temperature.

Another embodiment of the present invention includes an electro-opticdevice comprising: (i) an electro-optic polymer core comprising a firsthost polymer and a first nonlinear optical chromophore; and (ii) acladding comprising a second host polymer and a second nonlinear opticalchromophore; wherein the first nonlinear optical chromophore has astructure according to the general formula (I):

D-Π-A  (I)

wherein D represents a first organic electron-donating group; Arepresents a first organic electron-accepting group having an electronaffinity greater than the electron affinity of D; and Π represents afirst bridge covalently bonded to A and D; wherein the second nonlinearoptical chromophore has a structure according to the general formula(II):

D′-Π′-A′  (II)

wherein D′ represents a second organic electron-donating group which isthe same as D; A′ represents a second organic electron-accepting groupwhich is the same as A and has an electron affinity greater than theelectron affinity of D′; and Π′ represents a second bridge covalentlybonded to A′ and D′; and wherein the second bridge is less conjugatedthan the first bridge such that the cladding has an index of refractionthat is less than an index of refraction of the electro-optic polymercore, and wherein the second non-linear optical chromophore is presentin the second host polymer in a concentration such that the cladding hasa conductivity equal to or greater than at least 10% of the conductivityof the electro-optic polymer core at a poling temperature.

In various embodiments of the present invention, the cladding comprisesan upper cladding and a lower cladding, wherein the electro-opticpolymer core is disposed between the lower cladding and the uppercladding, wherein the lower cladding comprises the second host polymerand the second nonlinear optical chromophore and the upper claddingcomprises a third host polymer and a third nonlinear opticalchromophore; wherein the third nonlinear optical chromophore has astructure according to the general formula (III):

D″-Π″-A″  (III)

wherein D″ represents a third organic electron-donating group; A″represents a third organic electron-accepting group having an electronaffinity greater than the electron affinity of D″; and Π″ represents athird bridge covalently bonded to A″ and D″; wherein the upper claddinghas an index of refraction that is less than an index of refraction ofthe electro-optic polymer core, and wherein the third nonlinear opticalchromophore is present in the third host polymer in a concentration suchthat the cladding has a conductivity equal to or greater than at least10% of the conductivity of the electro-optic polymer core at a polingtemperature.

In various preferred embodiments of the present invention, the firsthost polymer, the second host polymer and the third host polymer are thesame. In various preferred embodiments of the present invention, thecladdings have a blue-shifted absorption spectrum as compared to theabsorption spectrum of the electro-optic polymer core. Additionally, invarious embodiments of the present invention, the second nonlinearoptical chromophore and/or the third nonlinear optical chromophore canbe present in the second host polymer and/or the third host polymer,respectively, in concentrations such that the respective claddinglayer(s) has (have) a conductivity equal to or greater than at least 20%of the conductivity of the electro-optic polymer core at a polingtemperature, and with increasing preference, a conductivity equal to orgreater than at least 30%, ≥40%, ≥50%, ≥60%, ≥70%, ≥80%, ≥90%, or 100%,of the conductivity of the electro-optic polymer core at a polingtemperature

An exemplary first nonlinear optical chromophore suitable for use inaccordance with the various embodiments of the present invention isrepresented by formula (Ia):

wherein the first bridge Π is represented by the formula IVa:

and the second and/or third bridges Π′ and Π″ are each independentlyrepresented by formula IVb or IVc:

Still other various embodiments in accordance with the present inventioninclude methods of preparing cladding materials for electro-opticdevices, which methods comprise: (a) selecting a first nonlinear opticalchromophore of the general formula (I):

D-Π-A  (I)

wherein D represents a first organic electron-donating group; Arepresents a first organic electron-accepting group having an electronaffinity greater than the electron affinity of D; and Π represents afirst bridge covalently bonded to A and D; and dispersing a first amountof the first nonlinear optical chromophore in a first host polymer toform an electro-optic core material; (b) measuring an index ofrefraction of the electro-optic core material, and measuring aconductivity of the electro-optic core material at a poling temperature;(c) selecting a second nonlinear optical chromophore of the generalformula (II):

D′-Π′-A′  (II)

wherein D′ represents a second organic electron-donating group, A′represents a second organic electron-accepting group having an electronaffinity greater than the electron affinity of D′, and Π′ represents asecond bridge covalently bonded to A′ and D′ and wherein the secondbridge is less conjugated than the first bridge; (d) dispersing a secondamount of the second nonlinear optical chromophore in a second hostpolymer to form an initial cladding material such that the secondnonlinear optical chromophore is present in the second host polymer atthe same concentration as the first nonlinear optical chromophore in thefirst host polymer; (e) measuring an index of refraction of the initialcladding material and a conductivity of the initial cladding material atthe poling temperature; (f) confirming that the index of refraction ofthe initial cladding material is lower than the index of refraction ofthe electro-optic core material; and (g) adjusting the concentration ofthe second nonlinear optical chromophore in the second host polymer toform a final cladding material having a conductivity equal to or greaterthan at least 10% of the conductivity of the electro-optic core materialat the poling temperature, while maintaining an index of refractionsuitable for the specific mode(s) of a desired waveguide.

In various preferred embodiments of methods and devices of the presentinvention, D and D′ are the same and A and A′ are the same. In variouspreferred embodiments of methods and devices of the present inventionwherein the cladding comprises a lower cladding and an upper cladding,D, D′ and D″ are the same and A, A′ and A″ are the same.

Other aspects, features and advantages will be apparent from thefollowing disclosure, including the detailed description, preferredembodiments, and the appended claims.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the invention, will be better understood whenread in conjunction with the appended drawings. For purposes ofillustration only, there are shown in the drawings embodiments which areexemplary and in no way limiting. It should be understood, that thevarious embodiments of the invention are not limited to the precisearrangements and instrumentalities shown.

In the drawings:

FIG. 1 is cross-sectional diagrammatic view of the general structure ofan electro-optic polymer modulator;

FIG. 2 is a graphical representation of the calibrated absorptionspectra of three nonlinear optical chromophores in accordance with oneembodiment of the present invention;

FIG. 3 is a graphical representation of resistivity as a function ofpoling field for an electro-optic core material and three claddingmaterials in accordance with an embodiment of the present invention;

FIG. 4 is a graphical representation of the index of refraction of acladding material in accordance with an embodiment of the presentinvention as a function of the concentration of nonlinear opticalchromophore in the host polymer; and

FIG. 5 is a graphical representation of the calibrated absorptionspectra of two nonlinear optical chromophores in accordance with anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the singular terms “a” and “the” are synonymous and usedinterchangeably with “one or more” and “at least one,” unless thelanguage and/or context clearly indicates otherwise. Accordingly, forexample, reference to “a solvent” or “the solvent” herein or in theappended claims can refer to a single solvent or more than one solvent.Additionally, all numerical values, unless otherwise specifically noted,are understood to be modified by the word “about.”

The present invention relates to electro-optic polymer devicescomprising: an electro-optic core material, i.e., a host-guest systemmade of a host polymer (e.g., a polyetherimide) and a guest nonlinearoptical chromophore, or multiple guest chromophores, or monolith of achromophore, or a polymers with chromophores in their main chains orside chains; and a cladding according to various embodiments of thepresent invention. A nonlinear optical chromophore may also be referredto herein interchangeably and for brevity as simply “a chromophore.”Electro-optic device and/or system embodiments of the present inventioninclude phased array radar, satellite and fiber telecommunications,cable television (CATV), optical gyroscopes for application in aerialand missile guidance, electronic counter measure systems (ECM) systems,backplane interconnects for high-speed computation, ultrafastanalog-to-digital conversion, land mine detection, radio frequencyphotonics, spatial light modulation, all-optical (light-switching-light)signal processing, solar conversion and photovoltaic devices, whereinsuch devices include an electro-optic core material and a cladding inaccordance with one of the various embodiments of the present invention.

One example of an electro-optic device according to the presentinvention includes electro-optic modulators for telecommunications,wherein the modulator comprises an electro-optic core material and acladding in accordance with one of the various embodiments of thepresent invention. Additional examples of electro-optic structures anddevices which can employ cores and claddings in accordance with thevarious embodiments of the present invention are known and describedthroughout the literature, including for example, Seong-Ku Kim, H.Zhang, D. H. Chang, et al., Electroooptic Polymer Modulators With anInverted-Rib Waveguide Structure, IEEE PHOTONICS TECHNOLOGY LETTERS,Vol. 15, No. 2, 218-220; Youngqiang Shi, Weiping Lin, David J. Olson, etal., Electro-optic polymer modulators with 0.8 V half-wave voltage,APPLIED PHYSICS LETTERS, Vol. 77, No 1, 1-3; H. Chen, B. Chen, D. Huang,et al., Broadband electro-optic polymer modulators with highelectro-optic activity and low poling optical loss, APPLIED PHYSICSLETTERS, Vol. 93, 043507; and David Eng, “Organic-Based Electro-OpticModulators for Microwave Photonic Applications,” Ph.D. Thesis,University of Delaware, 2015, the entire contents of each of which isincorporated herein by reference.

Referring, for example to FIG. 1, the general structure of anelectro-optic polymer modulator is depicted. An electro-optic core 10with an optional central ridge can be sandwiched or interposed betweenan upper (or “top”) cladding 40 and a lower (or “bottom”) cladding 45. Alower (or “bottom”) electrode 30 and an upper (or “top”) electrode 32are interposed by the lower cladding 45, electro-optic core 10, andupper cladding 40. The entire stack may be formed on a silicon wafer 50or other suitable substrates such as GaAs, InP and other Group III-Vmaterials such as GaN-on-Si, which substrates may also include aninsulating layer 52, such as silicon dioxide.

Thus, for example, still referring to the general structure depicted inFIG. 1, in one embodiment according to the present invention, the core10 comprises a first host polymer and a first nonlinear opticalchromophore; and the top and bottom claddings 40, 45 comprise a secondhost polymer and a second nonlinear optical chromophore; wherein thefirst nonlinear optical chromophore has a structure according to thegeneral formula (I):

D-Π-A  (I)

wherein D represents a first organic electron-donating group; Arepresents a first organic electron-accepting group having an electronaffinity greater than the electron affinity of D; and Π represents afirst bridge covalently bonded to A and D; wherein the second nonlinearoptical chromophore has a structure according to the general formula(II):

D′-Π′-A′  (II)

wherein D′ represents a second organic electron-donating group which isthe same as D; A′ represents a second organic electron-accepting groupwhich is the same as A and has an electron affinity greater than theelectron affinity of D′; and Π′ represents a second bridge covalentlybonded to A′ and D′; and wherein the second bridge is less conjugatedthan the first bridge such that the cladding has an index of refractionthat is less than an index of refraction of the electro-optic polymercore, and wherein the second non-linear optical chromophore is presentin the second host polymer in a concentration such that the conductivityof the cladding is equal to or greater than the conductivity of theelectro-optic polymer core at a poling temperature. In certain examplesof various preferred embodiments of the present invention, the first andsecond host polymers are also the same.

Electro-optic devices in accordance with the various embodiments of thepresent invention can be prepared by numerous known processes ofdeposition, coating and patterning, including CVD, PECVD, sputtering,spin-coating, polishing, etching and metallization whereby eachsuccessive layer is deposited sequentially upon the starting substrate.

As used herein, the term “nonlinear optic chromophore” (NLOC) refers tomolecules or portions of a molecule that create a nonlinear optic effectwhen irradiated with light. The chromophores are any molecular unitwhose interaction with light gives rise to the nonlinear optical effect.The desired effect may occur at resonant or nonresonant wavelengths. Theactivity of a specific chromophore in a nonlinear optic material isstated as its hyper-polarizability, which is directly related to themolecular dipole moment of the chromophore. Thus, nonlinear opticalchromophores suitable for use in core or cladding materials of thevarious embodiments according to the present invention include compoundscontaining an electron-donating group and an electron-accepting groupcovalently bonded to an intervening bridging group, or “bridge.”

Suitable electron-accepting groups “A” (also referred to in theliterature as electron-withdrawing groups) for nonlinear opticalchromophores in accordance with the various embodiments of the presentinvention include those described in published U.S. Patent Applications:US 2007/0260062; US 2007/0260063; US 2008/0009620; US 2008/0139812; US2009/0005561; US 2012/0267583A1 (collectively referred to as “the priorpublications”), each of which is incorporated herein by reference in itsentirety; and in U.S. Pat. Nos. 6,716,995; 6,584,266; 6,393,190;6,448,416; 6,44,830; 6,514,434; 5,044,725; 4,795,664; 5,247,042;5,196,509; 4,810,338; 4,936,645; 4,767,169; 5,326,661; 5,187,234;5,170,461; 5,133,037; 5,106,211; and 5,006,285; each of which is alsoincorporated herein by reference in its entirety.

In various nonlinear optical chromophores in accordance with variouspreferred embodiments of the present invention, suitableelectron-accepting groups include those according to general formula(Va):

wherein R² and R³ each independently represents a moiety selected fromthe group consisting of H, substituted or unsubstituted C₁-C₁₀ alkyl,substituted or unsubstituted C₂-C₁₀ alkenyl, substituted orunsubstituted C₂-C₁₀ alkynyl, substituted or unsubstituted aryl,substituted or unsubstituted alkylaryl, substituted or unsubstitutedcarbocyclic, substituted or unsubstituted heterocyclic, substituted orunsubstituted cyclohexyl, and (CH₂)_(n)—O—(CH₂)_(n) where n is 1-10. Invarious particularly preferred embodiments, the electron-accepting groupis

Suitable electron-donating groups “D” for nonlinear optical chromophoresin accordance with the various embodiments of the present inventioninclude those described in published U.S. Patent Applications: US2007/0260062; US 2007/0260063; US 2008/0009620; US 2008/0139812; US2009/0005561; US 2012/0267583A1 (collectively referred to as “the priorpublications”), each of which is incorporated herein by reference in itsentirety; and in U.S. Pat. Nos. 6,716,995; 6,584,266; 6,393,190;6,448,416; 6,44,830; 6,514,434; 5,044,725; 4,795,664; 5,247,042;5,196,509; 4,810,338; 4,936,645; 4,767,169; 5,326,661; 5,187,234;5,170,461; 5,133,037; 5,106,211; and 5,006,285; each of which is alsoincorporated herein by reference in its entirety.

Nonlinear optical chromophores according to the present invention canfurther comprise one or more pendant spacer groups bound the bridge, theelectron-donating group and/or the electron-accepting group. Pendantspacer groups in accordance with the present invention are generallynonreactive moieties which extend outward from the chromophore andcreate steric hindrance (i.e., “spacing”) between two or more of thechromophore molecules in a material containing the chromophores, andthus serve to prevent aggregation during and after poling.

Suitable bridges (H) for nonlinear optical chromophores according to thevarious embodiments of the present invention are organic moietiescontaining charge-transporting groups and having at least one endcapable of bonding to a D group and at least one end capable of bondingto an A group, and include those described in the previouslyincorporated references. Suitable charge-transporting groups includegroups disclosed in, for example, Shirota and Kageyama, CHEM. REV. 2007,107, 953-1010, the entire contents of which are hereby incorporated byreference herein, and include, for example, arylamines, in particulartriarylamines; and heteroaromatics, including fused and oligomericheteroaromatics such as oligothiophene or fused thiophenes, as well asphthalocyanine-based compounds, porphyrin-based compounds,azobenzene-based compounds, benzidine-based compounds, arylalkane-basedcompounds, aryl-substituted ethylene-based compounds, stilbene-basedcompounds, anthracene-based compounds, hydrazone-based compounds,quinone-based compounds, and fluorenone-based compounds.

In various preferred embodiments, bridging groups (Π) for non-linearoptical chromophores include those of the general formula (IV):

wherein X represents a substituted or unsubstituted, branched orunbranched C₂-C₄ diyl moiety; wherein a represents an integer of from 0to 3; and each of b and c independently represents an integer of from 0to 5, more preferably 0 to 2; and with the proviso that a+b+c is equalto or greater than 1.

As used herein throughout this specification and in the appended claims,the phrase “less conjugated than” means, in the broadest sense, lessextensive conjugation. More particularly, and in the various embodimentsaccording to the present invention, “less conjugated than” means lessconjugation, whether conjugation by virtue of alternating carbon-carbondouble bonds or the presence of a heteroatom with a lone pair ofelectrons, along the shortest path between the electron-donating groupand the electron-accepting group. Thus, for clarity and non-limitingexemplary purposes, the following bridge structures of Formulae X¹, X²,and X³ are all less conjugated than the bridge structure of Formula Y:

That is, due to the presence of the thiophene ring and its sulfurheteroatom, Formula Y is more conjugated than the structures of FormulaeX¹, X², and X³, along the shortest path between the electron-donatinggroup and the electron-accepting group (represented in the aboveformulae by the wavy lines).

Thus, for example, in various preferred embodiments, the first bridge(H) may have at least one more carbon-carbon double bonds within thebridge moiety than the bridge in the second and/or third nonlinearoptical chromophores. More specifically, for example, where the firstbridge (H) is represented by the formula IVa:

the bridge in the second and/or third nonlinear optical chromophore maybe represented by the formula IVb:

As a further example, an entire heterocyclic aromatic group can beremoved, such that where the first bridge (H) is represented by theformula IVa, the bridge in the second and/or third nonlinear opticalchromophore may be represented by the formula IVc:

Another example of a first nonlinear optical chromophore in accordancewith an embodiment of the present invention is represented by Formula(V):

Another example of a second nonlinear optical chromophore with a lessconjugated bridge in accordance with an embodiment of the presentinvention is represented by Formula (Va):

Measured indices of refraction for the nonlinear optical chromophores ofFormulae (V) and (Va) are set forth below in Table 1.

TABLE 1 n_TM n_TM Thick- (1309 (1548 ness Sample layers Substrate nm)nm) (μm) MTSi-7 HF7113 (25.1%)- Si/SiO2(2.0 1.6376 1.6247 2.022 APC150um), 4″ MTSi-8 HF7114 (25.1%)- Si/SiO2(2.0 1.6639 1.6406 2.141 APC150um), 4″

Referring to FIG. 5, the absorption spectra of the chromophores ofFormulae (V) and (Va) are graphically depicted.

Suitable host polymers into which a nonlinear optical chromophoresaccording to any of the various embodiments of the invention may beincorporated include amorphous polymers, such as, for example:polyetherimides (PEI); poly(methylmethacrylate)s (PMMA); polyimides;polyamic acid; polystyrenes; poly(urethane)s (PU); and amorphouspolycarbonates (APC). In various preferred embodiments the host polymercomprises a polyetherimide. Preferred amorphous host polymers have highTg values, low optical loss and good adhesion. The nonlinear opticalchromophores are generally incorporated within the host polymer at aloading of 1% to 99% by weight, based on the entire nonlinear opticalmaterial, more preferably at a loading of 5% to 50% by weight.

The first-order hyperpolarizability (β) is one of the most common anduseful NLO properties. Higher-order hyperpolarizabilities are useful inother applications such as all-optical (light-switching-light)applications. To determine if and to what extent a material, such as acore material or a cladding, includes a nonlinear optical chromophorewith first-order hyperpolar character, the following test may beperformed. First, the material in the form of a thin film is placed inan electric field to align the dipoles. This may be performed bysandwiching a film of the material between electrodes, such as indiumtin oxide (ITO) substrates, gold films, or silver films, for example.

To generate a poling electric field, an electric potential is thenapplied to the electrodes while the material is heated to near its glasstransition (T_(g)) temperature. After a suitable period of time, thetemperature is gradually lowered while maintaining the poling electricfield. Alternatively, the material can be poled by corona poling method,where an electrically charged needle at a suitable distance from thematerial film provides the poling electric field. In either instance,the dipoles in the material tend to align with the field.

The nonlinear optical property of the poled material is then tested asfollows. Polarized light, often from a laser, is passed through thepoled material, then through a polarizing filter, and to a lightintensity detector. If the intensity of light received at the detectorchanges as the electric potential applied to the electrodes is varied,the material incorporates a nonlinear optic chromophore and has anelectro-optically variable refractive index. A more detailed discussionof techniques to measure the electro-optic constants of a poled filmthat incorporates nonlinear optic chromophores may be found in Chia-ChiTeng, Measuring Electro-Optic Constants of a Poled Film, in NonlinearOptics of Organic Molecules and Polymers, Chp. 7, 447-49 (Hari SinghNalwa & Seizo Miyata eds., 1997), herein incorporated by reference inits entirety.

The relationship between the change in applied electric potential versusthe change in the refractive index of the material may be represented asits EO coefficient r₃₃. This effect is commonly referred to as anelectro-optic, or EO, effect.

The second-order hyperpolarizability (γ) or third-order susceptibility(χ⁽³⁾), are the normal measures of third-order NLO activity. While thereare several methods used to measure these properties, degeneratefour-wave mixing (DFWM) is very common. See C. W. Thiel, “For-waveMixing and Its Applications,”http://www.physics.montana.edu.students.thiel.docs/FWMixing.pdf, theentire contents of which are hereby incorporated herein by reference.Referring to Published U.S. Patent Application No. US 2012/0267583A1,the entire contents of which are incorporated herein by reference, amethod of evaluating third-order NLO properties of thin films, known inthe art as Degenerate Four Wave Mixing (DFWM), can be used. In FIG. 4 ofUS 2012/0267583A1, Beams 1 and 2 are picosecond, coherent pulses,absorbed by the NLO film deposited on a glass substrate. Beam 3 is aweaker, slightly delayed beam at the same wavelength as Beams 1 and 2.Beam 4 is the resulting product of the wave mixing, diffracted off ofthe transient holographic grating, produced by interferences of beams 1and 2 in the NLO material of the film. Beam 3 can be a “control” beam ata telecom wavelength which produces a “signal” beam at a frequency notabsorbed by the NLO material. Optical properties and stability ofnonlinear optical chromophores in accordance with the variousembodiments of the present invention can be measured, for example, asdescribed in US 2012/0267583A1.

Nonlinear optical chromophores in accordance with the various preferredembodiments of the present invention can be synthesized usingcommercially available reagents and reactions, as described below.Synthetic routes for other suitable non-linear optical chromophores aredescribed within the references previously incorporated herein, and areknown to those of ordinary skill in the art.

For example, 3,4-ethylenedioxythiophene and (4-(diethylamino)phenyl)methanol can each be obtained commercially from Sigma-Aldrich, orsynthesized by methods known in the art. In a first preliminary step, aphosphonium salt ylide of an electron-donating group is formed. Forexample, an electron-donating group precursor, such as(4-(diethylamino)phenyl)methanol, can be reacted with triphenylphosphinein the presence of acetic acid and hydrobromic or hydroiodic acid in asolvent such as dichloromethane to formN,N-diethylaniline-4-methylenephosphonium bromide or iodide.

In a second preliminary step, an aldehyde of a thiophene bridging groupis formed. For example, a thiophene bridging group, such as3,4-ethylenedioxythiophene, is reacted with dimethylformamide in thepresence of phosphoryl chloride to form3,4-ethylenedioxythiophene-2-aldehyde.

Next, using a Wittig reaction, the thiophene bridging group aldehydederivative can be reacted with the phosphonium salt ylide to form analkene adduct thereof. For example,3,4-ethylenedioxythiophene-2-aldehyde can be reacted withN,N-diethylaniline-4-methylenephosphonium bromide the resulting alkene(A):

The alkene adduct (A) can then be reacted with n-butyl lithium intetrahydrofuran, followed by reaction with an acrolein such as3-(N,N-dimethylamino)acrolein to form intermediate (B):

or alternatively reacted with dimethylformamide in the presence ofphosphoryl chloride to form intermediate (C):

The thiophene bridging group/electron-donating group adduct aldehyde,e.g., intermediate (B) or intermediate (C), can then be reacted with anelectron-accepting group, for example, via a Knoevenagel reaction, toreplace the aldehyde with a carbon-carbon double bond linking the adductto the electron accepting group.

Various embodiments of the present invention also include methodspreparing cladding materials for electro-optic devices, which methodscomprise: (a) selecting a first nonlinear optical chromophore of thegeneral formula (I):

D-Π-A  (I)

as previously described; and dispersing a first amount of the firstnonlinear optical chromophore in a first host polymer to form anelectro-optic core material. Methods in accordance with variousembodiments of the invention then include (b) measuring an index ofrefraction of the electro-optic core material, and measuring aconductivity of the electro-optic core material at a poling temperature.Indices of refraction can be measured by various known techniques,including, for example, by using an optical system based onprism-coupling, such as described in R. Ulrich and R. Torge,“Measurement of Thin Film Parameters with a Prism Coupler,” APPLIEDOPTICS, Vol. 12, No 12, 2901-2908. Conductivities of polymer films canbe determined by measuring current across the film sandwiched between aground electrode and a top electrode under a bias. The bias is set sothat the electric field is the same as the poling field.

Suitable poling temperatures are dependent upon the host polymer chosenand the concentration of the chromophore, and are generally determinedby monitoring heat flow as a function of temperature using differentialscanning calorimertry for temperature profile. For example, when usingvarious polyetherimides, a suitable poling temperature is from 185° C.to 210° C.

In various embodiments according to the present invention, methods nextinclude (c) selecting a second nonlinear optical chromophore of thegeneral formula (II):

D′-Π′-A′  (II)

as previously described, (d) dispersing a second amount of the secondnonlinear optical chromophore in a second host polymer to form aninitial cladding material such that the second nonlinear opticalchromophore is present in the second host polymer at the sameconcentration as the first nonlinear optical chromophore in the firsthost polymer, and (e) measuring an index of refraction of the initialcladding material and a conductivity of the initial cladding material atthe poling temperature. Next, the methods include (f) confirming thatthe index of refraction of the initial cladding material is lower thanthe index of refraction of the electro-optic core material. Preferably,for single mode applications, the index of refraction of the initialcladding material is lower than the index of refraction of theelectro-optic core material by an amount of from about 0.01 to about0.08.

Finally, various embodiments of methods in accordance with the presentinvention include (g) adjusting the concentration of the secondnonlinear optical chromophore in the second host polymer to form a finalcladding material having a conductivity equal to or greater than theconductivity of the electro-optic core material at the polingtemperature.

In various preferred embodiments of the methods according to the presentinvention, the absorption spectrum of the materials are measured at thewavelengths of interest, for example, 0.8 μm to about 2.0 μm. Suchpreferred methods include verifying that the initial cladding materialhas a blue-shifted absorption spectrum as compared to the absorptionspectrum of the core material. Optical loss of the cladding material islower when the spectrum is blue-shifted in comparison to the corematerial. Thus, in various preferred embodiments of the presentinvention, the cladding, both the upper and/or lower cladding, has ablue-shifted absorption spectrum compared to that of the core material.

Various embodiments of the invention will now be described in furtherdetail with reference to the following non-limiting examples.

EXAMPLES Example 1: Synthesis of a Non-Linear Optical Chromophore inAccordance with an Embodiment of the Invention

Step 1): A round bottom flask was charge with N,N-diethylaniline (29.8mL), triphenylphosphine (29.8 g), potassium iodide (31.2 g), chloroform(940 mL), acetic acid (37.6 mL) and formaldehyde (37% aqueous, 36.6 mL).The reaction was stirred at 50° C. for 60 hours under nitrogen. Aftercooling, the phases were separated, the organic portion was evaporatedand the residue crystallized from ethanol providingN,N-diethylaniline-4-methylenephosphomiun iodide in 74% yield, 92% pure.

Step 2): A round bottom flask was charged with dichloromethane (600 mL),N,N-dimethylformamide (10.4 mL) and phosphoryl chloride (12.6 mL). Thereaction was stirred under N₂ for 1 hour. 3,4-ethylenedioxythiophene(17.5 g) was added and stirring continued for 24 hours. Aqueous sodiumhydroxide (1N, 100 mL) was added and the reaction was stirred overnight.The phases were separated, dichloromethane dried with magnesium sulfateand evaporated. The resulting solid was dissolved in hot ethyl acetate,set aside to cool then filtered providing3,4-ethylenedioxythiophene-2-aldehyde as yellow needles, 27.7 g, 98%yield, 98% pure.

Step 3): A round bottom flask was charged with3,4-ethylenedioxythiophene-2-aldehyde (8.91 g),N,N-diethylaniline-4-methylenephosphomiun iodide (27.9 g),dichloromethane (255 mL) and sodium hydroxide (50% aqueous, 51 mL). Thereaction was vigorously stirred overnight. The phases where separated,the dichloromethane solution was dried with magnesium sulfate thenevaporated giving a honey colored syrup. The syrup crystallized uponsetting. The mixture was triturated in ether and filtered removing 85%of the triphenylphosphine oxide. The filtrate was evaporated and theresidue chromatographed on silica gel eluting with hexane/ethyl acetate(3:1). The appropriate fractions were combined and evaporated giving(E)-4-(2-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)vinyl)-N,Ndiethylbenzenamineas a thick yellow syrup which crystalized upon setting, 14.1 g, 95%yield, 96% pure.

Step 4):(E)-3-(7-((E)-4-(diethylamino)styryl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)acrylaldehyde:A round bottom flask was charged with(E)-4-(2-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)vinyl)-N,Ndiethylbenzenamine(2.28g) and THF (20 mL). The mixture was chilled to −70° C. then n-Butyllithium(2.5N in hexane, 3.5 mL) was added and the reaction was stirredat 0° C. for 30 minutes. The 3-(N,Ndimethylamino) acrolein (1.0 mL) wasadded and the reaction was stirred another 30 minutes at 0° C. The stillcold reaction was quenched with water, diluted with ethyl acetate,washed with brine, dried with magnesium sulfate and evaporated. Theresidue was chromatographed with ethyl acetate/hexane(1:3-1:2). Theappropriate fractions were combined and evaporated giving(E)-3-(7-((E)-4-(diethylamino)styryl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)acrylaldehydeas a red powder, 2.10 g, 74% yield, cis to trans ratio 1:9, 91% pure.

Step 5): 3-(3,4-dichlorophenyl)-3-hydroxybutan-2-one: A dried roundbottom flask was evacuated and filled with nitrogen three times thencharged with 2,3-butanedione (4.38 mL) and tetrahydrofuran (250 mL).While under nitrogen the solution was chilled to 0° C. then3,4-dichlorophenylmagnesium bromide (0.5 N in tetrahydrofuran, 50 mL)was added in a steady stream by cannula using nitrogen pressure. The icebath was removed and the reaction was stirred under nitrogen for 1 hour.The reaction was quenched with saturated ammonium chloride, diluted withethyl acetate, washed with water then brine, dried with magnesiumsulfate and evaporated giving3-(3,4-dichlorophenyl)-3-hydroxybutan-2-one as a thick syrup. The crudeproduct was used without purification.

Step 6): A dry round bottom flask was charged with3-(3,4-dichlorophenyl)-3-hydroxybutan-2-one (5.80 g), malononitrile(3.30 g) then the flask was evacuated and charged with nitrogen threetimes. Anhydrous ethanol (65 mL) was added then lithium ethoxide (1N inethanol, 2.5 mL) was added. A Soxhlet extractor, with a thimble filledwith molecular sieves, was added and the reaction was refluxed undernitrogen overnight. After 24 hours the reaction was allowed to cool,neutralized with 1N hydrochloric acid to a pH of ˜6, diluted with ethylacetate, washed with water then brine, dried with magnesium sulfate andevaporated giving a thick past. Chromatography (silica gel, CHCl₃) gavea light yellow powder. The powder was refluxed in ethanol, allowed tocool, filtered, washed with ethanol and dried giving3-cyano-2-(dicyanomethylene)-4,5-dimethyl-5-(3,4-dichlorophenyl)-2,5-dihydrofuranas a yellow powder, 4.80 g, 52% yield (for two steps, 5 & 6), 94% pure.

Step 7): A round bottom flask was charged with(E)-3-(7-((E)-4-(diethylamino)styryl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)acrylaldehyde(3.43 g),3-Cyano-2-(dicyanomethylene)-4,5-dimethyl-5-(3,4-dichlorophenyl)-2,5-dihydrofuran(3.62 g), tetrahydrofuran (40 mL), ethanol (10 mL) and piperidine (0.2mL). The reaction was stirred at 80° C. for 24 hours. The reaction wasevaporated. The residue was chromatographed on silica gel eluting withdichloromethane. The appropriate fractions were combined and evaporated.The residue was re-chromatographed on silica gel eluting withhexane/ethyl acetate. The cleanest fractions were combined andevaporated. The residue was dissolved in dichloromethane andcrystallized by evaporation. The crystals were soaked in etherovernight. The ether was decanted off and fresh ether added, daily, forfour more days. Fresh ether was added, again, followed by trituration,filtration, wash with ether and drying gave3-cyano-2-(dicyanomethylene)-4-((1E,3E)-4-(7-((E)-4-(diethylamino)styryl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)buta-1,3-dienyl))-5-methyl-5-(3,4-dichlorophenyl)-2,5-dihydrofuran(I″) as very fine copper colored crystals, 1.44 g, 22% yield, 100%trans, 99% pure.

Example 2: Synthesis of a Non-Linear Optical Chromophore with a LessConjugated Bridge (M1) in Accordance with an Embodiment of the Invention

Step 1):

N,N-diethylaniline-4-methylenephosphomiun bromide: A round bottom flaskwas charged with N,N-diethylaniline (29.8 mL), triphenylphosphine (29.8g), potassium iodide (31.2 g), chloroform (940 mL), acetic acid (37.6mL) and formaldehyde (37% aqueous, 36.6 mL). The reaction was stirred at50° C. for 60 hours under nitrogen. After cooling, the phases wereseparated, the organic portion was evaporated and the residuecrystallized from ethanol providing the target compound in 74% yield,92% pure.

Step 2):

3,4-ethylenedioxythiophene-2-aldehyde: A round bottom flask was chargedwith dichloromethane (600 mL), N,N-dimethylformamide (10.4 mL) andphosphoryl chloride (12.6 mL). The reaction was stirred under N₂ for 1hour. The 3,4-ethylenedioxythiophene (17.5 g) was added and stirringcontinued for 24 hours. The aqueous sodium hydroxide (1N, 100 mL) wasadded and the reaction was stirred overnight. The phases were separated,dichloromethane dried with magnesium sulfate and evaporated. Theresulting solid was dissolved in hot ethyl acetate, set aside to coolthen filtered providing the target compound as yellow needles, 27.7 g,98% yield, 98% pure.

Step 3):

(E)-4-(2-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)vinyl)-N,N-diethylbenzenamine:A round bottom flask was charged with3,4-ethylenedioxythiophene-2-aldehyde (8.91 g),N,N-diethylaniline-4-methylenephosphomiun bromide (27.9 g),dichloromethane (255 mL) and sodium hydroxide (50%, aqueous, 51 mL). Thereaction was vigorously stirred overnight. The phases where separated,the dichloromethane solution was dried with magnesium sulfate thenevaporated giving a honey colored syrup. The syrup crystallized uponsetting. The mixture was triturated in ether and filtered removing 85%of the triphenylphosphine oxide. The filtrate was evaporated and theresidue chromatographed on silica gel eluting with hexane/ethyl acetate(3:1). The appropriate fractions were combined and evaporated giving athick yellow syrup the crystallized upon setting, 14.1 g, 95% yield, 96%pure.

Step 4):

(E)-7-(4-(diethylamino)styryl)-2,3-dihydrothieno[3,4-b][1,4]dioxine-5-carbaldehyde:A round bottom flask was charged with dichloromethane (1 L),N,N-dimethylformamide (12.7 mL) and phosphoryl chloride (15.4 mL). Thereaction was stirred under nitrogen for 1 hour. The(E)-4-(2-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)vinyl)-N,N-diethylbenzenamine(47.3 g) was added and stirring continued for 24 hours. LCMS indicatedcomplete conversion to the iminium salt. The 1N aqueous sodium hydroxide(300 mL) was added and the reaction was stirred overnight. The phaseswere separated, dichloromethane dried with magnesium sulfate andevaporated. The resulting solid was dissolved in hot ethyl acetate, setaside to cool and filtered providing the target compound as red/orangeneedles, 49.4 g, 96% yield, 97% pure.

Step 5):

3-(3,4-dichlorophenyl)-3-hydroxybutan-2-one: A dried round bottom flaskwas evacuated and filled with nitrogen three times then charged with2,3-butanedione (4.38 mL) and tetrahydrofuran (250 mL). While undernitrogen the solution was chilled to 0° C. then3,4-dichlorophenylmagnesium bromide (0.5 N in tetrahydrofuran, 50 mL)was added in a steady stream by cannula using nitrogen pressure. The icebath was removed and the reaction was stirred under nitrogen for 1 hour.The reaction was quenched with saturated ammonium chloride, diluted withethyl acetate, washed with water then brine, dried with magnesiumsulfate and evaporated giving a thick syrup. The crude product was usedwithout purification.

Step 6):

3-Cyano-2-(dicyanomethylene)-4,5-dimethyl-5-(3,4-dichlorophenyl)-2,5-dihydrofuran:A dry round bottom flask was charged with3-(3,4-dichlorophenyl)-3-hydroxybutan-2-one (5.80 g), malononitrile(3.30 g) then the flask was evacuated and charged with nitrogen threetimes. Anhydrous ethanol (65 mL) was added then lithium ethoxide (1N inethanol, 2.5 mL) was added. A Soxhlet extractor, with a thimble filledwith molecular sieves, was added and the reaction was refluxed undernitrogen overnight. After 24 hours the reaction was allowed to cool,neutralized with 1N hydrochloric acid to a pH of ˜6, diluted with ethylacetate, washed with water then brine, dried with magnesium sulfate andevaporated giving a thick past. Chromatography (silica gel, CHCl₃) gavea light yellow powder. The powder was refluxed in ethanol, allowed tocool, filtered, washed with ethanol and dried giving the desired furanderivative as a yellow powder, 4.80 g, 52% yield (for two steps, 5 & 6),94% pure.

Step 7):

2-[3-cyano-5-(3,4-dichlorophenyl)-4-[(E)-2-[7-[(E)-2-[4-(diethylamino)phenyl]vinyl]-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl]vinyl]-5-methyl-2-furylidene]propanedinitrile(PKM1): A round bottom flask was charged with(E)-3-(7-((E)-4-(diethylamino)styryl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)acrylaldehyde(1.30 g),3-Cyano-2-(dicyanomethylene)-4,5-dimethyl-5-(3,4-dichlorophenyl)-2,5-dihydrofuran(1.24 g), ethanol (150 mL) and piperidine (31 mg). The reaction wasstirred at 80° C. for 20 hours. The reaction was evaporated. The residuewas chromatographed on silica gel eluting with hexane/ethyl acetate. Thecleanest fractions were combined and evaporated. The residue wascrystallized from ethanol giving the product as very fine copperypowder, 1.69 g, 68% yield, 100% trans, 97% pure.

Example 3: Synthesis of a Non-Linear Optical Chromophore with a LessConjugated Bridge (M0) in Accordance with an Embodiment of the Invention

Step 1):

N,N-diethyl(4)aniline aldehyde: A round bottom flask was charged withdichloromethane (600 mL), N,N-dimethylformamide (10.4 mL) and phosphorylchloride (12.6 mL). The reaction was stirred under N₂ for 1 hour. TheN,N-diethylaniline (17.5 g) was added and stirring continued for 24hours. LCMS indicated complete conversion to the iminium salt. Theaqueous sodium hydroxide (1N, 100 mL) was added and the reaction wasstirred overnight. The phases were separated, dichloromethane dried withmagnesium sulfate and evaporated. The resulting oil was dissolved inether, filtered through Celite and evaporated providing the targetcompound as yellow oil, 27.7 g, 98% yield, 98% pure.

Step 2):

3-(3,4-dichlorophenyl)-3-hydroxybutan-2-one: A dried round bottom flaskwas evacuated and filled with nitrogen three times then charged with2,3-butanedione (4.38 mL) and tetrahydrofuran (250 mL). While undernitrogen the solution was chilled to 0° C. then3,4-dichlorophenylmagnesium bromide (0.5 N in tetrahydrofuran, 50 mL)was added in a steady stream by cannula using nitrogen pressure. The icebath was removed and the reaction was stirred under nitrogen for 1 hour.The reaction was quenched with saturated ammonium chloride, diluted withethyl acetate, washed with water then brine, dried with magnesiumsulfate and evaporated giving a thick syrup. The crude product was usedwithout purification.

Step 3):

3-Cyano-2-(dicyanomethylene)-4,5-dimethyl-5-(3,4-dichlorophenyl)-2,5-dihydrofuran:A dry round bottom flask was charged with3-(3,4-dichlorophenyl)-3-hydroxybutan-2-one (5.80 g), malononitrile(3.30 g) then the flask was evacuated and charged with nitrogen threetimes. Anhydrous ethanol (65 mL) was added then lithium ethoxide (1N inethanol, 2.5 mL) was added. A Soxhlet extractor, with a thimble filledwith molecular sieves, was added and the reaction was refluxed undernitrogen overnight. After 24 hours the reaction was allowed to cool,neutralized with 1N hydrochloric acid to a pH of ˜6, diluted with ethylacetate, washed with water then brine, dried with magnesium sulfate andevaporated giving a thick past. Chromatography (silica gel, CHCl₃) gavea light yellow powder. The powder was refluxed in ethanol, allowed tocool, filtered, washed with ethanol and dried giving the desired furanderivative as a yellow powder, 4.80 g, 52% yield (for two steps, 5 & 6),94% pure.

Step 4):

2-[3-cyano-5-(3,4-dichlorophenyl)-4-[(E)-2-[4-(diethylamino)phenyl]vinyl]-5-methyl-2-furylidene]propanedinitrile(PKM0): A round bottom flask was charged with4-(diethylamino)benzaldehyde (44 mg),3-Cyano-2-(dicyanomethylene)-4,5-dimethyl-5-(3,4-dichlorophenyl)-2,5-dihydrofuran(82 mg), pyridine (2.5 mL) and acetic acid (10 g). The reaction wasstirred for 3 days. The reaction was evaporated. The residue waschromatographed on silica gel eluting with hexane/DCM (20%). Thecleanest fractions were combined and evaporated. The residue wascrystallized from DCM giving the product as very fine golden powder, 24mg, 77% yield, 98% pure.

Example 4: Measurement of the Absorption Spectra of the NonlinearOptical Chromophores Prepared in Examples 1, 2 and 3

Referring to FIG. 2, the absorption spectra for the nonlinear opticalchromophores prepared in examples 1, 2 and 3 are depicted graphically.As can be seen from FIG. 2, the nonlinear optical chromophores having aless conjugated bridge have blue-shifted absorption spectra. The spectrawere taken from dilute solution of the chromophores in dichloromethaneusing a Cary 50 UV-Vis spectrometer was used for the measurements.

Example 5: Preparation of Core Material and Cladding MaterialsIncorporating the Nonlinear Optical Chromophores Prepared in Examples 1,2 and 3

Each of the nonlinear optical chromophores prepared in examples 1, 2 and3 was combined with Ultem® 1000P polyetherimide and approximately 1.4 wt% of dichloromethane and 1,2,3-trichloropropane mixture (1:4 by volume)in varying nonlinear optical chromophore concentrations to formsolutions of the materials. The nonlinear optical chromophore of Example1 was prepared as a single 22.5 wt % solution, based on solids. Thenonlinear optical chromophore of Example 2 was prepared as threesolutions of 23%, 20% and 18% concentrations. The nonlinear opticalchromophore of Example 3 was prepared as a single 24.4% solution.

Example 6: Measurement of Indices of Refraction, Optical Loss, andConductivities of Core Material and Cladding Materials Prepared inExample 5

The index of refraction and optical loss (at 1309 nm and at 1548 nm) aswell as the conductivity of each of the materials prepared in Example 5were measured as described previously herein. The optical loss wasmeasured by using a system prism-coupling a laser beam as describedpreviously herein into a polymer coating on a silicon wafer with anoxide layer of about 2.5 μm. The intensity of scattered light as thebeam propagated through the coating was recorded by scanning a bundle ofoptical fiber along the propagation of the beam above the coating. Thedecay of the scattered light was fit to an exponential curve tocalculate the loss of the beam. The measured values are set forth belowin Table 2.

TABLE 2 1309 nm 1548 nm Conduc- loss loss tivity* Coatings n_TM (dB/cm)n_TM (dB/cm) (S/cm) M2 (22.5%) - 1.729 8 1.701 2.2 1.3 × 10⁻⁹ Core M1(18.0%) - 1.685 1.8 1.673 N/A 5.0 × 10⁻⁹ Cladding M0 (24.4%) - 1.685 11.676 1.4 1.1 × 10⁻⁹ Cladding *At a standard poling temperature andfield.

Referring to FIG. 3, the resistivity of various materials from Example6, sandwiched between an ITO coated glass and a gold top electrodeplaced on a hot plate set at a poling temperature of 197° C., is plottedagainst the poling field. As can be seen from FIG. 3, the resistivity ofthe chromophores with less conjugated bridges is lower and thus, theirconductivity higher at all poling fields measured.

Referring to FIG. 4, the index of refraction of the three solutions ofthe nonlinear optical chromophore of Example 2 as measured in thisexample are plotted. As shown in FIG. 4, the index of refraction can beadjusted by adjusting the concentration of the nonlinear opticalchromophore in the host polymer.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

What is claimed is:
 1. An electro-optic device comprising: (i) anelectro-optic polymer core comprising a first host polymer and a firstnonlinear optical chromophore; and (ii) a cladding comprising a secondhost polymer and a second nonlinear optical chromophore; wherein thefirst nonlinear optical chromophore has a structure according to thegeneral formula (I):D-Π-A  (I) wherein D represents a first organic electron-donating group;A represents a first organic electron-accepting group having an electronaffinity greater than the electron affinity of D; and Π represents afirst bridge covalently bonded to A and D; wherein the second nonlinearoptical chromophore has a structure according to the general formula(II):D′-Π′-A′  (II) wherein D′ represents a second organic electron-donatinggroup; A′ represents a second organic electron-accepting group having anelectron affinity greater than the electron affinity of D′; and Π′represents a second bridge covalently bonded to A′ and D′; and whereinthe cladding has an index of refraction that is less than an index ofrefraction of the electro-optic polymer core, and wherein the secondnonlinear optical chromophore is present in the second host polymer in aconcentration such that the cladding has a conductivity equal to orgreater than at least 10% of the conductivity of the electro-opticpolymer core at a poling temperature.
 2. The electro-optic deviceaccording to claim 1, wherein the cladding comprises an upper claddingand a lower cladding, wherein the electro-optic polymer core is disposedbetween the lower cladding and the upper cladding, wherein the lowercladding comprises the second host polymer and the second nonlinearoptical chromophore and the upper cladding comprises a third hostpolymer and a third non-linear optical chromophore; wherein the thirdnonlinear optical chromophore has a structure according to the generalformula (III):D″-Π″-A″  (III) wherein D″ represents a third organic electron-donatinggroup; A″ represents a third organic electron-accepting group having anelectron affinity greater than the electron affinity of D″; and Π″represents a third bridge covalently bonded to A″ and D″; wherein theupper cladding has an index of refraction that is less than an index ofrefraction of the electro-optic polymer core, and wherein the thirdnonlinear optical chromophore is present in the third host polymer in aconcentration such that the cladding has a conductivity equal to orgreater than at least 10% of the conductivity of the electro-opticpolymer core at the poling temperature.
 3. The electro-optic deviceaccording to claim 2, wherein the first host polymer, the second hostpolymer and the third host polymer are the same.
 4. The electro-opticdevice according to claim 3, wherein the lower cladding and the uppercladding each has a blue-shifted absorption spectrum as compared to theabsorption spectrum of the electro-optic polymer core.
 5. Anelectro-optic device comprising: (i) an electro-optic polymer corecomprising a first host polymer and a first nonlinear opticalchromophore; and (ii) a cladding comprising a second host polymer and asecond nonlinear optical chromophore; wherein the first nonlinearoptical chromophore has a structure according to the general formula(I):D-Π-A  (I) wherein D represents a first organic electron-donating group;A represents a first organic electron-accepting group having an electronaffinity greater than the electron affinity of D; and Π represents afirst bridge covalently bonded to A and D; wherein the second nonlinearoptical chromophore has a structure according to the general formula(II):D′-Π′-A′  (II) wherein D′ represents a second organic electron-donatinggroup which is the same as D; A′ represents a second organicelectron-accepting group which is the same as A and has an electronaffinity greater than the electron affinity of D′; and Π′ represents asecond bridge covalently bonded to A′ and D′; and wherein the secondbridge is less conjugated than the first bridge such that the claddinghas an index of refraction that is less than an index of refraction ofthe electro-optic polymer core, and wherein the second non-linearoptical chromophore is present in the second host polymer in aconcentration such that the cladding has a conductivity equal to orgreater than at least 10% of the conductivity of the electro-opticpolymer core at a poling temperature.
 6. The electro-optic deviceaccording to claim 5, wherein the cladding comprises an upper claddingand a lower cladding, wherein the electro-optic polymer core is disposedbetween the lower cladding and the upper cladding, wherein the lowercladding comprises the second host polymer and the second nonlinearoptical chromophore and the upper cladding comprises a third hostpolymer and a third non-linear optical chromophore; wherein the thirdnonlinear optical chromophore has a structure according to the generalformula (III):D″-Π″-A″  (III) wherein D″ represents a third organic electron-donatinggroup which is the same as D; A″ represents a third organicelectron-accepting group which is the same as A and has an electronaffinity greater than the electron affinity of D″; and Π″ represents athird bridge covalently bonded to A″ and D″ and which is the same as Π′;wherein the upper cladding has an index of refraction that is less thanan index of refraction of the electro-optic polymer core, and whereinthe third nonlinear optical chromophore is present in the third hostpolymer in a concentration such that the cladding has a conductivityequal to or greater than at least 10% of the conductivity of theelectro-optic polymer core at the poling temperature.
 7. Theelectro-optic device according to claim 5, wherein the second nonlinearoptical chromophore is present in the second host polymer in aconcentration such that the cladding has a conductivity equal to orgreater than at least 50% of the conductivity of the electro-opticpolymer core at a poling temperature.
 8. The electro-optic deviceaccording to claim 5, wherein the second nonlinear optical chromophoreis present in the second host polymer in a concentration such that thecladding has a conductivity equal to or greater than the conductivity ofthe electro-optic polymer core at a poling temperature.
 9. Theelectro-optic device according to claim 6, wherein the third nonlinearoptical chromophore is present in the third host polymer in aconcentration such that the cladding has a conductivity equal to orgreater than at least 50% of the conductivity of the electro-opticpolymer core at the poling temperature.
 10. The electro-optic deviceaccording to claim 6, wherein the third nonlinear optical chromophore ispresent in the third host polymer in a concentration such that thecladding has a conductivity equal to or greater than the conductivity ofthe electro-optic polymer core at the poling temperature.
 11. Theelectro-optic device according to claim 6, wherein the first hostpolymer, the second host polymer and the third host polymer are thesame.
 12. The electro-optic device according to claim 6, wherein thelower cladding and the upper cladding each has a blue-shifted absorptionspectrum as compared to the absorption spectrum of the electro-opticpolymer core.
 13. The electro-optic device according to claim 11,wherein the lower cladding and the upper cladding each has ablue-shifted absorption spectrum as compared to the absorption spectrumof the electro-optic polymer core.
 14. The electro-optic deviceaccording to claim 1, further comprising a first electrode and a secondelectrode interposed by the electro-optic polymer core and the cladding.15. The electro-optic device according to claim 6, further comprising afirst electrode and a second electrode interposed by the lower cladding,the electro-optic polymer core and the upper cladding.
 16. Theelectro-optic device according to claim 6, wherein Π representsstructure according to the formula IVa:

wherein Π′ and Π″ each represent a structure according to the formulaIVb:


17. The electro-optic device according to claim 6, wherein H representsstructure according to the formula IVa:

wherein Π and Π″ each represent a structure according to the formulaIVc:


18. The electro-optic device according to claim 16, wherein each of A,A′ and A″ represents an electron-accepting group according to theformula Va:

and wherein each of D, D′ and D″ represents an electron-donating groupaccording to the formula Vd:


19. The electro-optic device according to claim 17, wherein each of A,A′ and A″ represents an electron-accepting group according to theformula Va:

and wherein each of D, D′ and D″ represents an electron-donating groupaccording to the formula Vd:


20. A method of preparing cladding materials for electro-optic devices,said method comprising: (a) selecting a first nonlinear opticalchromophore of the general formula (I):D-Π-A  (I) wherein D represents a first organic electron-donating group;A represents a first organic electron-accepting group having an electronaffinity greater than the electron affinity of D; and Π represents afirst bridge covalently bonded to A and D; and dispersing a first amountof the first nonlinear optical chromophore in a first host polymer toform an electro-optic core material; (b) measuring an index ofrefraction of the electro-optic core material, and measuring aconductivity of the electro-optic core material at a poling temperature;(c) selecting a second nonlinear optical chromophore of the generalformula (II):D′-Π-A′  (II) wherein D′ represents a second organic electron-donatinggroup, A′ represents a second organic electron-accepting group having anelectron affinity greater than the electron affinity of D′, and Π′represents a second bridge covalently bonded to A′ and D′ and whereinthe second bridge is less conjugated than the first bridge; (d)dispersing a second amount of the second nonlinear optical chromophorein a second host polymer to form an initial cladding material such thatthe second nonlinear optical chromophore is present in the second hostpolymer at the same concentration as the first nonlinear opticalchromophore in the first host polymer; (e) measuring an index ofrefraction of the initial cladding material and a conductivity of theinitial cladding material at the poling temperature; (f) confirming thatthe index of refraction of the initial cladding material is lower thanthe index of refraction of the electro-optic core material; and (g)adjusting the concentration of the second nonlinear optical chromophorein the second host polymer to form a final cladding material having aconductivity equal to or greater than at least 10% of the conductivityof the electro-optic polymer core material at the poling temperature.21. The method according to claim 20, wherein D and D′ are the same andwherein A and A′ are the same.
 22. The method according to claim 20,wherein the first host polymer and the second host polymer are the same.23. The method according to claim 22, wherein D and D′ are the same andwherein A and A′ are the same.
 24. An electro-optic device comprising anelectro-optic core material and a final cladding material prepared bythe method according to claim 20.